Many electronic devices, such as smart phones, laptop or tablet computers, kiosks, among many others, have a display that also functions as a touch sensitive input surface. A user can apply a localized input force, either with a finger, stylus or other means, to the input surface to effect an actuation, such as of a selection from a menu, or to alter the electronic device's operation. The applied input force is often detected or measured by the electronic device by means of one or more sensors positioned beneath the input surface (i.e., opposite to the exterior side of the input surface that faces the user).
Strain sensors are one type of sensor sometimes used to detect the applied input force. These function by detecting a strain (i.e., a displacement) in either the input surface or a structural layer connected to the input surface. However, to decrease the weight and thickness of the electronic device, its internal components are often placed very close together. If in addition the size of the display is increased, its input surface may show greater compliance or ability to bend. If the input surface or its structural layers bend or deflect too much they may contact other internal components, such as a rigid battery, and be unable to deflect further. In such situations, a strain sensor may not be able to provide reliable values of the applied input force. It may nevertheless be useful for the electronic device to be able to detect a greater range of applied input forces. The embodiments disclosed herein are directed to overcoming this and other limitations.